Electronic analogue watches are known in which the hour hand and the minute hand for display of the current time are driven either by the same electric motor or by separate electric motors, which cause the wheels of the timepiece mechanism to advance step by step. In both cases it can occur that motor steps are lost because of shocks applied to the watch, the presence of electromagnetic fields or other external interferences. The consequence of this is that, although the internal clock of the watch delivers a correct indication of the current time, the hour and minute hands deliver a distorted indication of this current time, because the motors have jumped several steps under the effect of the external interference applied to the watch. It is therefore necessary to re-synchronise the position of the hour and minute hands either initiated by application software or initiated by the user.
To enable this synchronisation to occur, the watch is equipped with a device for detecting the position of the hour wheel and of the minute wheel. At a predetermined time or when initiated by the user, a control circuit orders the hour wheel and the minute wheel to advance. This control must occur sequentially, i.e. one wheel after the other. During the course of this advancing movement, the hour wheel and the minute wheel each pass through a determined position, in which the device for detecting the position is activated, and this allows the position of the hour and minute wheels to be known with precision. The control circuit then calculates the position of the wheel, compares it to the value supplied by the internal clock of the watch and deducts from these operations the number of motor steps that have to be applied to the hour and minute wheels to bring the hands for displaying the current time to the proper position on the dial of the watch.
A known solution for detecting the position of a wheel of a timepiece mechanism for an electronic analogue watch consists of arranging a light source that emits a light beam and a light detection system on either side of the disc of the wheel. The light source and the light detection system are arranged to face one another and a hole is provided in the disc of the wheel on the path of the light source and the light detection system. When the hole arrives at the level of the light source, the light beam passes through the hole and falls on the light detection system, which allows a precise indication of the position of the wheel to be provided.
Such a device for detecting and synchronising the position of a wheel of a timepiece mechanism for an electronic analogue watch has several disadvantages. The first of these disadvantages lies in the fact that the light source and the light detection system are arranged in tiers in an essentially vertical direction, which makes the detection and synchronisation device bulky and requires spaces to be provided to the top and to the bottom. The second problem critically arises in the case where it is sought to detect the position of two wheels mounted coaxially, as is the case with an hour wheel and a minute wheel. In fact, in such a situation it is necessary, for example, to arrange the two light detection devices between the two wheels and to position the light sources respectively above and below the assembly of the two coaxial wheels. Such an arrangement is not only bulky but additionally requires two of the elements of the detection devices, e.g. the two light detection devices, to be positioned between the wheels, which makes automation of the production of such timepiece movements practically impossible.